[Zope] DTMLFile, the mysterious animal

[Oliver Bleutgen]

Can somebody explain to me what really happens when I have a method in 
my product like
DTMLFile('www/main.dtml', globals(), filter='Image').

My problem is that I want to modify the stock main.dtml in order to show 
only a subset of contained objects, so I change the line
<dtml-in objectItems ...>
to
<dtml-in "objectItems(filter)" ...>

and now I get a TypeError, "object of type 'list' is not callable"

I know that something like OrderedFolder etc. might do what I want, but 
I'm curious about what really happens here.

cheers,
oliver